The invention relates to a method for obtaining images by means of magnetic resonance (MR) of an object placed in a static magnetic field comprising the following steps
generation of an excitation RF pulse in a part of the body, PA1 measurement of a plurality of sets of MR signals using a plurality of receiver coils along a trajectory in k-space comprising a first plurality of lines by application of a read gradient and other gradients, PA1 reconstruction of a final image from a combination of the plurality of sets of MR signals measured and distance dependent sensitivities of the plurality of receiver coils. The invention further relates to an MR apparatus arranged for performing such method. In this patent application pixels mean picture elements of a digital image, voxels mean volume-elements of a three-dimensional digital object. PA1 that the final image is reconstructed from a combination of the receiver coil images and the distance dependent sensitivities of the receiver coils. In t his way the reconstruction of the final image does not depend on a specific sensitivity function of the sets of receiver coils and can be applied for an arbitrary set of receiver coils and the restrictions on the size of the field of view and the orientation of the slice to be image are less severe. Furthermore, non-integer reduction factors can be chosen. This option gives a possibility to shift aliasing artefacts to less important parts of the image. Simultaneous or partly simultaneous measurement of the MR data sets yields a reduction in the acquisition time and a possibility of fast MR imaging compared to conventional MR-imaging.
Such a method is known from the article "Simultaneous Acquisition of Spatial Harmonic (SMASH): Fast Imaging with radio frequency Coil Array" by D. K. Sodickson et al, published in Magnetic Resonance in Medicine, vol. 38, page 591-603, 1997. The known method is used, for example, in real time cardiac imaging of human beings. To reduce the acquisition time of MR data in the known method a sub-encoding data acquisition scheme is used wherein the plurality of sets of MR signals are simultaneously measured using the plurality of receiver coils along the trajectory in k-space containing the first plurality of lines using the read gradient and the other gradients. The number of lines corresponds to a reduced number phase-encoding steps in comparison with a number of phase encoding steps in conventional Fourier MR imaging. The receiver coils may be arranged in an array of surface coils. A final MR data set is determined from a specific distance sensitivity function of the set of receiver coils and the sets of MR signals measured. The final MR data set then contains the information of the number of lines of the conventional Fourier MR imaging. The final image is then reconstructed by transforming the final MR data set. The number of sets of MR signals may be equal to the number of receiver coils in the array. Furthermore, the specific distance sensitivity function of the set of receiver coils must have a sinusoidal shape. By the simultaneous measurement of MR data is the acquisition time is reduced. The reduction factor is determined by the number of lines in k-space corresponding to the final image and the number of lines which the sub-encoding data acquisition employs. The reduction in the acquisition time may, for example, enable application in real time cardiac imaging or functional imaging. A disadvantage of the known method is that it may be limited to only a few positions of a field of view and a limited number of orientations of the slice of the object to be image because of the specific sensitivity function of the set of coils. The field of view is defined by a distance in a phase encoding direction covered by the trajectory in the k-space.